In the two-dimensional positioning and machining devices, especially the modern semiconductor micromachining equipments, and other ultra-precision machining equipments, the high-precise movement is typically implemented by the planar motor. The planar motor has attracted much attention in both the academe and the industry because of its advantages such as its quick response, high sensitivity and simple structure. Chinese Patents No. 201110045692.8, No. 200910029368.X and No. 200910088894.3 have described several types of planar motors with different structures in detail.
Currently, the detection for the rotor position of the planar motor is usually performed by the optical measurement method such as using the grating and the laser interferometer. According to Chinese Patent No. 200880111964.6, the movement measurement for the planar motor is performed with a two-dimensional grating, in which a planar grating of a larger area is required to be installed in the planar motor so as to generate optical signals with displacement information to communicate with optical sensors, and the requirement for operating environment is higher, and the surfaces of the grating ruler must be protected and prevented from being polluted; according to Chinese Patent No. 201110040403.5, the grating sensor is adopted to detect the moving position in two directions, and in each direction, a main scale and its corresponding reading head, which must meet the measuring range requirement, are required to be installed to generate Moire fringe signals or other types of optical signals with the displacement information, and the requirement for operating environment is also high; and according to Chinese Patent No. 200910029828.9, a laser position sensor is adopted to perform measurement for movement of the planar motor through laser triangulation methods or echo analysis, but the preciseness of the measurement is strongly affected by the environment, and it is difficult to guarantee high preciseness under long moving range and the signal processing is not simple and quick at the same time.
Therefore, it is desirable to develop a newly planar motor rotor displacement measuring method, which has advantages of reducing complexity of installation of the sensor, having high preciseness under long moving range and simple and quick signal processing.